This invention relates to a pressure-reducing valve for high-pressure gas cylinders employed when taking out a high-pressure gas contained in a high-pressure gas cylinder.
When storing a gas such as hydrogen gas for fuel cell systems, a high-pressure gas cylinder containing highly compressed gas is ordinarily used. When taking out the gas from the high-pressure gas cylinder, the gas pressure is reduced down to the intended pressure through a pressure-reducing valve and the gas filled in the cylinder is taken out.
Hereupon, the gas contained in the cylinder is filled in at an extremely high pressure (e.g., approximately 70 MPa) in order to increase a gas loadage, and consequently it is impossible to reduce the pressure with high accuracy to the intended secondary pressure by just one pressure reducing operation. However, by employing a two-step pressure reducing method, the second pressure reducing mechanism can set the gas pressure up as the intended secondary pressure with high accuracy.
Such a two-step pressure reducing mechanism is already known in, for example, Unexamined Japanese Patent Publication No. 2000-257797.
However, the above-mentioned pressure reducing mechanism ordinary used requires a supply channel to supply a gas from a high-pressure gas cylinder to the pressure reducing mechanism. In case that the gas is a fuel gas, the shorter such a supply channel for a high-pressure gas is, the higher safety it has, assuming the case of breakage by an external impact such as an accident. The patent literature 1 describes a mechanism that two pressure-reducing valves are integrated in a cylinder valve. When employing such an integration of a two-step pressure reducing mechanism for a pressure reduction of a high-pressure gas, there exist the following problems.
A frequency of vibration of a valve element is increased when reducing a pressure of a high-pressure gas, and therefore loads applied to each part are increased due to the vibration. Further, a two-step pressure reducing mechanism requires two valve elements, and therefore loads applied to the entire pressure reducing mechanism is further increased by vibrations generated by these two vibratory sources. For this reason, constituent parts have become easily broken and a failure frequency has been increased.
The object of the invention is to provide a pressure-reducing valve for a high-pressure gas and particularly to provide a two-step pressure-reducing valve usable for a long term.